Examples of display devices include cathode ray tubes (CRTs), liquid crystal display (LCD) devices using an optical effect of electric field, plasma display panels (PDPs) using gas discharge, and electro luminescence display (ELD) devices using a light emitting effect of an electric field. Among them, research on the LCD devices is in active progress.
Since the LCD devices have advantages of a small size, lightweight, low power consumption, and full colors to overcome limitations of CRTs, fields to which the LCD devices are applied gradually extend.
Since the LCD devices are light receiving devices adjusting an amount of light received from the outside to display an image, they require a separate external light source such as a light unit.